This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2001-363406 filed on Nov. 28, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to an antenna device. More particularly, the present invention pertains to an antenna which is provided inside of a door handle for opening and closing a door, for communicating with an outside.
A known antenna device is disclosed in Japanese Patent Laid-Open Publication No. 2001-308629. The disclosed device is shown in FIGS. 6, 7.
An antenna device 51, which is used as a part of a keyless entry device of a vehicle, is provided inside of a door handle 52 for opening a vehicle door 60. The antenna device 51 includes a first antenna 55 and a second antenna 58. The first antenna 55 includes a coil 54 wound around a ferrite core 53 and a resonant capacitor C6 connected to the ferrite core 53 in parallel which constitutes a parallel resonant circuit. The second antenna 58 includes a circular coil 56 accommodating therein the ferrite core 53, a link coil 57 which is formed by one end portion of the circular coil 56 being wound a predetermined number of times around the ferrite core 53, and a resonant capacitor C7 connected to the circular coil 56 in series which constitutes a series resonant 5 circuit.
An axial direction of the circular coil 56 is provided perpendicular to an outer surface of the vehicle door. A magnetic field component Hy generated by the circular coil 56 extends in a direction, making an angle of 90 degrees relative to the vehicle door (y-direction in FIG. 7). The vehicle door is a conductive board so that an image of a magnetic field component xe2x88x92Hy in an opposite direction to the magnetic field component Hy is generated by the vehicle door. The magnetic field component Hy generated by the circular coil 56 is thus cancelled by the magnetic field component xe2x88x92Hy in the opposite direction. In order to solve this problem, the antenna device 51 is provided with an electromagnetic wave absorbing material 59 between the circular coil 56 and the vehicle door 60.
However, a number of parts is increased and an assembly condition is lowered by providing the electromagnetic wave absorbing material 59, which is also restricted by a size of the door handle.
Thus, a need exists for the antenna device which addresses at least the foregoing drawback associated with other known antenna devices.
It is an object of the present invention to provide an antenna device which can ensure a required magnetic field strength generated by an antenna without increasing a number of parts.
According to a first aspect of the present invention, the antenna device includes a door handle provided outside of a vehicle door for opening the vehicle door, and the antenna provided inside of the door handle and generating a magnetic field component in a direction different from a perpendicular direction to an outer surface of the vehicle door.
According to a second aspect of the present invention, the antenna includes a first antenna for generating a first magnetic field component and a second antenna for generating a second magnetic field component. The first magnetic field component is generated in approximately parallel to the outer surface of the vehicle door. The second magnetic field component is generated perpendicular to the first magnetic field component.
According to a third aspect of the present invention, the first antenna includes a first resonant circuit having a first coil which axial direction is in parallel to the outer surface of the vehicle door and a first resonant capacitor connected to the first coil. The second antenna includes a second resonant circuit having a second coil which axial direction is perpendicular to the axial direction of the first coil and provided outside of the first antenna, a link coil connected to the second coil and wound in the same direction as that of the first coil, and a second resonant capacitor connected to the link coil.
According to a fourth aspect of the present invention, the antenna further includes a third antenna for generating a third magnetic field component, a fourth antenna for generating a fourth magnetic field component, and a fifth antenna for generating a fifth magnetic field component. The third magnetic field component is generated in approximately parallel to the outer surface of the vehicle door. The fourth magnetic field component is generated perpendicular to the third magnetic field component. In addition, the fifth magnetic field component is generated in approximately parallel to the outer surface of the vehicle door and also perpendicular to the third magnetic field component.
According to a fifth aspect of the present invention, the third antenna includes a third resonant circuit having a third coil which axial direction is in parallel to the outer surface of the vehicle door and a third resonant capacitor connected to the third coil. The fourth antenna includes a fourth resonant circuit having a fourth coil which axial direction is perpendicular to the axial direction of the third coil and provided outside of the third antenna, a link coil connected to the fourth coil and wound in the same direction as that of the third coil, and a fourth resonant capacitor connected to the link coil. Further, the fifth antenna includes a fifth resonant circuit having a fifth coil provided inside of the third antenna and the fourth antenna and which axial direction is in parallel to the outer surface of the vehicle door and also perpendicular to the axial direction of the third coil.